.TH std::mask_array 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::mask_array \- std::mask_array

.SH Synopsis
   Defined in header <valarray>
   template< class T > class mask_array;

   std::mask_array is a helper template used by the valarray subscript operator with
   std::valarray<bool> argument. It has reference semantics and provides access to the
   subset of the valarray consisting of the elements whose indices correspond to true
   values in the std::valarray<bool> mask.

.SH Member types

   Type       Definition
   value_type T

.SH Member functions

   constructor   constructs a mask_array
                 \fI(public member function)\fP
   destructor    destroys a mask_array
                 \fI(public member function)\fP
   operator=     assigns contents
                 \fI(public member function)\fP
   operator+=
   operator-=
   operator*=
   operator/=
   operator%=    performs arithmetic operation on the array referred by mask.
   operator&=    \fI(public member function)\fP
   operator|=
   operator^=
   operator<<=
   operator>>=

.SH Example


// Run this code

 #include <iostream>
 #include <valarray>

 void println(auto rem, const auto& data)
 {
     for (std::cout << rem; int n : data)
         std::cout << n << ' ';
     std::cout << '\\n';
 }

 int main()
 {
     std::valarray<int> data{0, 1, 2, 3, 4, 5, 6, 7, 8, 9};

     println("Initial valarray: ", data);

     data[data > 5] = -1;
     // the type of data>5 is std::valarray<bool>
     // the type of data[data>5] is std::mask_array<int>

     println("After v[v>5]=-1:  ", data);
 }

.SH Output:

 Initial valarray: 0 1 2 3 4 5 6 7 8 9
 After v[v>5]=-1:  0 1 2 3 4 5 -1 -1 -1 -1

.SH See also

   simd_mask           data-parallel type with the element type bool
   (parallelism TS v2) \fI(class template)\fP
